What makes a steel 'aggressive'?

[Bolster]

I have just three Spyderco M4s at this point, not a huge sample size, but they seem to be more aggressive than other steels owned. Is this my imagination...are some steels really more aggressive, by which I mean, a sort of "eagerness to cut"? If so, what makes an 'aggressive' steel that way? And what other steels would you consider 'aggressive' to the level of M4 or beyond? Because I need more of this sort of cutting aggression...

[Pokey]

Larger, chunkier, carbides, where when the steel is sharpened the matrix is worn away a bit more between the carbides?

[p_atrick]

Larger, chunkier, carbides, where when the steel is sharpened the matrix is worn away a bit more between the carbides?

Larger in relation to what? I thought the PM process keeps the carbides small.

[ladybug93]

serrations

[vivi]

How you sharpen it.

Any steel can be made to cut aggressive.

[Bill1170]

I wish I knew. Steel is much-studied but still a mystery. Vivi and Ladybug are both correct, but there’s more to the story.

[Haunted House]

I tend to think of a course edge as an aggressive cutter. Serrated may be the most aggressive.

As far as an “aggressive steel”… I don’t know how to quantify that, although it does sorta feel like the edge that comes up on tool steels is a little more aggressive and nasty.
Cruwear gets nasty sharp (aggressive?) very easily.

[kennbr34]

Is that question what aggression is, or how aggression is achieved?

I'm no expert, but aggression in an edge to me means the edge has a kind of "sticky" and biting feeling when pressed to the skin, where it seems to grab at the epidermis with barely any pressure at all. Sometimes if you cut material that's under a tensile load like rope, fabric, sheets of plastic etc, it's almost as if it invades the material at a microscopic level and then causes it to pull apart under the tensile load without it needing to actually push or slice, but simply touching it. For example, if I open up a bag of cat food or feed, I like to pinch the corner and pull it so the material is being pulled on, and an "aggressive" knife will just touch it and cause it to separate along a naturally formed seam without any real exertion of pressure. Though, this definition of 'aggression' for me may also be conceived by how it is accomplished...

Which is just making the edge toothy, 'micro-serrated' or however else you want to phrase it. This is accomplished in a lot of different ways depending on the steel and abrasive used. I think simple, low-alloy, and softer steels tend to get their toothiness imparted by the grit level. Other steels like carbide-rich variety seem to have it naturally by merit of the carbides in the steel matrix. So that is one reason a lot of people will say "aggressive steel" because it tends to be harder to polish them into a smoother apex, and they generally remain aggressive even at higher grit levels. Ultimately though, however they're formed, they basically act like little needles that can penetrate material with extreme readiness because they're at such a small scale.

One empirical test I have done to support this in the past is with a BESS tester. Typically, people will see this as a test of a blade's push-cutting ability, and generally people will say that a highly polished edge is better at push-cutting than a very toothy/aggressive one. However, I have found in the past that I have been able to achieve higher BESS scores by using a very toothy edge, and loading the thread under high tension, so when the microscopic teeth just barely penetrate the test media, it immediately pulls apart and counts as being severed. I've gamed that system in such a way to get absurdly low BESS scores that weren't very representative of how sharp the knife would be if testing in good faith, but showcase how the micro-serrations definitely penetrate and cause taught material to pull apart.

I think the opposite is a "smooth" edge. I think it's basically the diametric opposite of an aggressive edge, and the best example is a straight razor. If a straight razor had micro-serrations, and you were to stretch the skin taught and put the blade to the skin, it would basically breach the dermis and cause a cut immediately--that might result in a large laceration opening up, or just irritation. But with a smooth apex, it can remain small enough to be so sharp it will shave a hair, but also be able to ride along the skin without causing too much damage.

That's why when I have gotten an edge that passes the hair-hanging test, it could be with a very highly polished and smoothed apex like on a straight razor, or it could also be on a very toothy and aggressive edge on a pocket knife. I think the main difference, though, is that while some may prefer a very smooth cutting edge on a pocket knife or utility knife, I can't imagine someone wanting to shave with an aggressive edge; it would just unnecessarily increase the risk of cuts without resulting in any performance benefit. On the other hand, I have heard some people on these forums (Doc Dan I believe) saying they have had good results using diamond abrasives to get a more aggressive straight razor edge, but I figure that's probably speaking relatively.

Just my $.02

[Naperville]

I am no steel or sharpening expert. I read what Larrin produces and make good use of the charts. I just know what I like and stick to buying carbide rich steels for knives under 6 inches if at all possible. Carbide rich steels are chosen for a reason, they cut better than the older non carbide steels, not just that they are newer.

As to BESS testers, they ONLY test what is under less than one millimeter of the knife blade and the remainder of the blade is ignored. I think Larrin has a better steel tester that slices cardboard test pieces, and that would be a better tester overall of how a knife edge is going to perform. I just don't know, will a BESS tester show that a high carbide steel cuts better? I do not think that is what it is measuring.

I could be wrong about Larrin's steel testing rig too, don't take my word for it.

What testing rig tests the quality of a cut, employing the length of a knife blade?

[JoviAl]

I have just three Spyderco M4s at this point, not a huge sample size, but they seem to be more aggressive than other steels owned. Is this my imagination...are some steels really more aggressive, by which I mean, a sort of "eagerness to cut"? If so, what makes an 'aggressive' steel that way? And what other steels would you consider 'aggressive' to the level of M4 or beyond? Because I need more of this sort of cutting aggression...

Is it because your 3 M4 knives are all PM2 Tantos? They are super aggressive

Joking aside, I find tool steels like Cruwear and K390 easily get that kind of nasty sharp, but funnily enough so does S90V One of life’s great mysteries. I suppose the only rational thing to do is increase your sample size to test empirically.

[eventhorizon]

Shout at it, tell it what a miserable little piece of bad steel it is!

[Erich]

I have just three Spyderco M4s at this point, not a huge sample size, but they seem to be more aggressive than other steels owned. Is this my imagination...are some steels really more aggressive, by which I mean, a sort of "eagerness to cut"? If so, what makes an 'aggressive' steel that way? And what other steels would you consider 'aggressive' to the level of M4 or beyond? Because I need more of this sort of cutting aggression...

It's your imagination. There is no such thing as an "aggressive" steel. Abrasives influence edge behavior. Diamond generally will give you a toothier edge better for draw cutting because of how diamond damages the edge at the expense of edge retention and push cutting. Water stones and ceramics will give you much better push cutting and a longer lasting edge than diamond because the edge isn't gouged out by the irregular diamond scratch pattern. However there is nothing in M4 that makes it inherently more "eager to cut" than 420hc or vg-10.

[Doc Dan]

I think it is the edge angle combined with how it is sharpened.

[juggler]

If I cut myself with a blade, then it's an aggressive steel. In my experience, all steels are pretty aggressive...

[Deadboxhero]

I have just three Spyderco M4s at this point, not a huge sample size, but they seem to be more aggressive than other steels owned. Is this my imagination...are some steels really more aggressive, by which I mean, a sort of "eagerness to cut"? If so, what makes an 'aggressive' steel that way? And what other steels would you consider 'aggressive' to the level of M4 or beyond? Because I need more of this sort of cutting aggression...

What is edge aggression?


If we set the edge on a material we are going to cut and use the lightest touch possible at very, very low speed to draw the edge across the material we are cutting and it slices into the material with great ease and depth that edge is said to be aggressive.

So if we wanted to quantify edge aggression.
We would need a to slice with a fixed load, fixed speed and fixed length on a known material with the same edge angle/finish/sharpness using the same sharpening stone on a range of samples and measure the depth cut.

The deeper depth in these circumstances would translate to more edge aggression if the other variables are controlled.

That's how you would quantify the edge aggression between the different steels/heat treatments.




Generally speaking, coarser edges will have more aggression because they make less surface contact at the apex, but it is a inverse relationship with edge stability.

[Giygas]

What is edge aggression?


If we set the edge on a material we are going to cut and use the lightest touch possible at very, very low speed to draw the edge across the material we are cutting and it slices into the material with great ease and depth that edge is said to be aggressive.

So if we wanted to quantify edge aggression.
We would need a to slice with a fixed load, fixed speed and fixed length on a known material with the same edge angle/finish/sharpness using the same sharpening stone on a range of samples and measure the depth cut.

The deeper depth in these circumstances would translate to more edge aggression if the other variables are controlled.

That's how you would quantify the edge aggression between the different steels/heat treatments.




Generally speaking, coarser edges will have more aggression because they make less surface contact at the apex, but it is a inverse relationship with edge stability.

I'm sure you're aware of him, but for those who aren't Pavol Sandor does some great testing using a rig he built to accomplish this general concept.

Here's his video for a 15v PM2:

[Deadboxhero]

What is edge aggression?


If we set the edge on a material we are going to cut and use the lightest touch possible at very, very low speed to draw the edge across the material we are cutting and it slices into the material with great ease and depth that edge is said to be aggressive.

So if we wanted to quantify edge aggression.
We would need a to slice with a fixed load, fixed speed and fixed length on a known material with the same edge angle/finish/sharpness using the same sharpening stone on a range of samples and measure the depth cut.

The deeper depth in these circumstances would translate to more edge aggression if the other variables are controlled.

That's how you would quantify the edge aggression between the different steels/heat treatments.




Generally speaking, coarser edges will have more aggression because they make less surface contact at the apex, but it is a inverse relationship with edge stability.

I'm sure you're aware of him, but for those who aren't Pavol Sandor does some great testing using a rig he built to accomplish this general concept.

Here's his video for a 15v PM2:

Nice, could you start a new thread and give us a summary of the testing?

That would be appreciated.

Check this out
https://www.reddit.com/r/sharpening/s/F3bVXoHKSE

[dj moonbat]

I think it's possible that some steels have enough of a carbide load that it could be like microscopic saw teeth. I don't think it's possible that we would notice that effect in daily use. Our senses just aren't that acute.

So for all practical purposes, vivi's right: the difference between aggressive and tame is the apexing and finishing.

[Deadboxhero]

I think it's possible that some steels have enough of a carbide load that it could be like microscopic saw teeth. I don't think it's possible that we would notice that effect in daily use. Our senses just aren't that acute.

So for all practical purposes, vivi's right: the difference between aggressive and tame is the apexing and finishing.

The sense of touch is more acute than we give it credit for, you'll often see sharpeners feeling the edge with their finger pads like the Carter three finger edge test.

https://www.sciencedaily.com/releases/2 ... 110853.htm

Dr. Mark Rutland and his research team in 2013 found that in testing people were able to detect an amplitude of 13 nanometers on a test surface.

[MFlovejp]

Just my two cents- I think personal sharpening style and technique plays a role, so some steels may be more “aggressive” or grabby or whatever for one person vs another individual. For me, it seems like ZDP, XHP, LC200N, BD1N, and to some extent Cruwear like to get this way with the stones and technique I sharpen most knives with.